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CTL(4) FreeBSD Kernel Interfaces Manual CTL(4)
NAMEctl -- CAM Target Layer
SYNOPSIS
To compile this driver into the kernel, place the following line in your
kernel configuration file:
devicectl
Alternatively, to load the driver as a module at boot time, place the
following line in loader.conf(5):
ctl_load="YES"
DESCRIPTION
The ctl subsystem provides SCSI target devices emulation. It supports
features such as:
+o Disk, CD-ROM and processor device emulation
+o Tagged queueing
+o SCSI task attribute support (ordered, head of queue, simple tags)
+o SCSI implicit command ordering support
+o Full task management support (abort, query, reset, etc.)
+o Support for multiple ports, initiators, targets and backing stores
+o Support for VMWare VAAI and Microsoft ODX offload (COMPARE AND WRITE,
XCOPY, POPULATE TOKEN/WRITE USING TOKEN, WRITE SAME and UNMAP)
+o Persistent reservation support
+o Extensive VPD/mode/log pages support
+o Featured error reporting, error injection and basic SMART support
+o High Availability clustering support with ALUA
+o All I/O handled in-kernel, no userland context switch overhead
The ctl subsystem includes multiple frontends to provide access using
different transport protocols and implementations:
camsim Provides access for local system via virtual initiator mode
CAM(4) SIM.
camtgt Provides access for remote systems via target mode CAM(4) SIMs,
such as Fibre Channel isp(4) and mpt(4).
cfumass Provides access for remote systems via USB Mass Storage Class
Bulk Only (BBB) Transport.
ha Internal frontend used to receive requests from other node ports
in High Availability cluster.
ioctl Provides access for local user-level applications via ioctl(2)
based API.
iscsi Provides access for remote systems via the iSCSI protocol using
cfiscsi(4).
tpc Internal frontend used to receive requests from Third Party Copy
engine, implementing copy offload operations.
The ctl subsystem includes two backends to create logical units using
different kinds of backing stores:
block Stores data in ZFS ZVOLs, files or raw block devices.
ramdisk Stores data in RAM, that makes it mostly useful for performance
testing. Depending on configured capacity can work as black
hole, thin or thick provisioned disk.
SYSCTL VARIABLES
The following variables are available as both sysctl(8) variables and
loader(8) tunables:
kern.cam.ctl.debug
Bit mask of enabled CTL log levels:
1 log commands with errors;
2 log all commands;
4 log data for commands other then READ/WRITE.
Defaults to 0.
kern.cam.ctl.ha_id
Specifies unique position of this node within High Availability
cluster. Default is 0 -- no HA, 1 and 2 -- HA enabled at speci-
fied position.
kern.cam.ctl.ha_mode
Specifies High Availability cluster operation mode:
0 Active/Standby -- primary node has backend
access and processes requests, while sec-
ondary can only do basic LUN discovery and
reservation;
1 Active/Active -- both nodes have backend
access and process requests, while secondary
node synchronizes processing with primary
one;
2 Active/Active -- primary node has backend
access and processes requests, while sec-
ondary node forwards all requests and data to
primary one;
All above modes require established connection between HA cluster
nodes. If connection is not configured, secondary node will
report Unavailable state; if configured but not established --
Transitioning state. Defaults to 0.
kern.cam.ctl.ha_peer
String value, specifying method to establish connection to peer
HA node. Can be "listen IP:port", "connect IP:port" or empty.
kern.cam.ctl.ha_link
Reports present state of connection between HA cluster nodes:
0 not configured;
1 configured but not established;
2 established.
kern.cam.ctl.ha_role
Specifies default role of this node:
0 primary;
1 secondary.
This role can be overridden on per-LUN basis using "ha_role" LUN
option, so that for one LUN one node is primary, while for
another -- another. Role change from primary to secondary for HA
modes 0 and 2 closes backends, the opposite change -- opens. If
there is no primary node (both nodes are secondary, or secondary
node has no connection to primary one), secondary node(s) report
Transitioning state. State with two primary nodes is illegal
(split brain condition).
SEE ALSOcfiscsi(4), cfumass(4), ctladm(8), ctld(8), ctlstat(8)HISTORY
The ctl subsystem first appeared in FreeBSD 9.1.
AUTHORS
The ctl subsystem was originally written by Kenneth Merry
<ken@FreeBSD.org>. Later work was done by
Alexander Motin <mav@FreeBSD.org>.
FreeBSD 11.1 March 29, 2017 FreeBSD 11.1